Unit 08 - Modeler

Graphical Modeler allows creating, editing, and managing complex models in easy-to-use graphical user interface. Using Graphical Modeler a chain of processes (ie. GRASS modules) can be wrapped into one process (a model). A model can be executed repeatedly with slightly different inputs or parameters.

Our first model will be based on Unit 05 - Simple computation. Actually the model will perform two operations:

  1. set mask based on vector cloud mask file (r.mask) and
  2. compute NDVI (i.vi)

Graphical Modeler can be launched from menu File ‣ Graphical modeler or by grass-modeler-main Graphical Modeler from main toolbar (or alternatively as g.gui.gmodeler module from console).


Fig. 59 Graphical Modeler.

GRASS modules can be added to the model from menu Model ‣ Add command or by grass-module-add Add command (GRASS module) to the model from main toolbar.


Fig. 60 Add commands (GRASS modules) to the model, in this case r.mask.

After adding r.mask module to the model let’s open its properties dialog by double-click and enter vector map to be used as a mask. Don’t forget to enable inverse mask by -i flag.


Fig. 61 Define parameters for r.mask, a vector map used for creating a mask.

In similar way will be added to the model the second command i.vi (properties dialog for this command is open automatically because there are required options which must be set).


Fig. 62 NDVI model version 1.

It’s good idea to set metadata for the model and enable overwriting data produced by model (Model ‣ Model properties).


Fig. 63 Define model properties and enable overwriting data produced by model.

Such model can be run repeatedly using different computation regions.


Current computation region can be changed quickly by Set computation region extent interactively from grass-zoom-more Various zoom options in Map Display.


Fig. 64 Change computation region before running the model.


Before changing the region it’s good idea to remove mask if exists from Raster ‣ Mask (by r.mask module).

r.mask -r

Now let’s run our model by grass-execute Run model. Progress is printed into Command output.


Fig. 65 Model computation progress.

After redrawing map display grass-layer-redraw Render map (assuming that we have already displayed raster map of NDVI in map display), we should see a difference.


Fig. 66 New NDVI raster map computed by the model.

Sample model to download: ndvi-v1.gxm